The triggering of a restraint arrangement in a motor vehicle may occur as a function of a variety of parameters, such as the seriousness of the collision and the position and the weight of the passengers. For that reason, not only the seat occupancy, but characteristic data for each individual occupant may be detected as well, which allows conclusions as to the weight of the occupant, so that each occupant may be assigned a weight classification. In practice, force sensors, which are installed in the individual seats, may be used to detect the characteristic data for such an occupant classification. The force sensors may be foil strain gauges for the direct measurement of weight. However, the force-sensor system may also be implemented in the form of a sensor mat having pressure-sensitive sensor cells, which are arranged in a matrix and may be activated individually, to detect the pressure distribution in the seat in the form of a value matrix. The heavier a person, the greater the depression of the seat material and the higher the number of activated sensor cells. Moreover, the pressure value per se detected by a sensor cell may be dependent on the respective pressurization. In the evaluation of the pressure data acquired by the individual sensor cells of the sensor mat, the number of the activated sensor cells may, therefore, be taken into account as well, in addition to the individual pressure values. A control device, which is likewise installed in the seat, may perform the evaluation. The result of the evaluation, namely the determined respective weight classification, may be forwarded to the air bag control device, so that in the triggering of the restraint arrangement the individual seat occupancy may be taken into account. This exemplary method may be largely independent of external conditions, such as cold or wear.
In conventional devices for passenger classification, features may be extracted from the continually detected pressure data with the aid of an appropriate algorithm, from which a filter, connected downstream from the algorithm, may then determine the weight classification. The filter parameters may be continually updated and selected such that the time progression of the earlier acquired and evaluated pressure data is also taken into account. The weight classification of an occupant is newly determined approximately every 0.7 s on the basis of the then current pressure data. If the algorithm recognizes that a seat is unoccupied for more than 5 s, the filter parameters are reset. This reset is initiated by a simple counter, which specifies the time interval of approx. 5 s.
In the conventional device, the information “seat not occupied” is transmitted to the air bag control device with the resetting of the filter. As soon as the air bag control device receives the information “seat not occupied”, the restraint arrangement for the respective seat is switched off, so that it is not triggered in a then occurring crash. This may often be problematic in practice, such as, for example, when a passenger briefly, but for longer than 5 s, gets up from his seat without exiting, for instance, to remove a coat while driving. In such a case, the air bag control device is supplied with the information “seat not occupied”, the restraint arrangement is switched off, and the respective occupant may be unprotected, or insufficiently protected, until the air bag control device is once again provided with a realistic estimated value for the weight classification of the occupant.
German Published Patent Application No. 199 32 520 describes a device for classifying persons or objects, which includes an arrangement for acquiring characteristic data on the person to be classified or the object to be classified, at least one algorithm extracting features from the instantaneously acquired characteristic data; at least one filter determining the classification of the person or object from the instantaneously extracted features, taking into account the time progression of the features extracted for the person to be classified or the object to be classified; and a first counter via which the resetting of the filter is initiated if the algorithm, during the first time interval specified by the first counter, has provided exclusively features for the non-presence of a person or an object.
German Published Patent Application No. 199 08 165 discusses an arrangement for acquiring characteristic data on the person to be classified or the object to be classified, the arrangement including video sensing, ultrasound sensing or radar sensing.
German Published Patent Application No. 195 46 297 discusses the sensing of the occupant position for determining the occupant size.
German Published Patent Application No. 42 12 018 discusses the classification of persons and objects in the motor vehicle, the person or the object being classified with respect to its weight.